1. Field of the Invention
The present invention relates to a system for heating, cooling and/or dehumidification, singly or in combination, of an environmental load, or heating or cooling a process load, by removing thermal energy from a first media and transferring that thermal energy to a second media for dissipation therein, wherein heat recovery may also be provided.
2. Description of the Related Art
In recent years, society has become ever more concerned about two major environmental conditioning issues. One of those issues involves the improvement of indoor air quality within certain facilities, such as residences, schools, hospitals, office buildings, retail stores, industrial facilities, and the like. The other one of those major issues involves the necessity of reducing the cost of energy required to provide environmental conditioning for such facilities. Since the early 1970's, considerable research has been expended on those two issues which has resulted in significant developments in new engineering standards for the design of systems to meet such needs.
Unfortunately, there exists an inherent problem when attempting to address both of these issues within any particular application. This problem results from the fact that the single most important factor in improving indoor air quality is the introduction of large amounts of outdoor air to refresh the otherwise enclosed space. In light of the fact that outdoor air is itself preferably conditioned before being supplied into the indoor space (i.e., heated, cooled and/or dehumidified), prior art processes typically result in significantly increasing operating costs for any particular facility. Therefore, it should be apparent that these two goals--refreshing with a sufficient quantity of outside air, and conditioning that outside air without significantly increasing operating costs--tend to be mutually limiting.
As noted, substantial research and development has gone into addressing these issues throughout the preceding decades. This collective work has resulted in the investigation of various approaches which can be generally categorized in two basic types: recuperative heat exchange processes, and regenerative heat exchange processes.
In recuperative heat exchange processes, two flowing heat exchange media are separated by a heat transfer surface. Heat is transferred from the media of the higher temperature via thermal conductance through the heat transfer surface into the lower temperature media. For example, apparatuses utilizing a recuperative heat exchange process include tube-in-shell, fin-tube and tube-in-tube heat exchangers.
In regenerative heat exchange processes, a heat exchange material is alternatively heated in a higher-temperature heat exchange media and then physically displaced to a lower-temperature heat exchange media where the material is cooled and the heat transferred away by the surrounding media. For example, apparatuses utilizing a regenerative heat exchange process include systems having rotating or tracking heat exchangers. Examples of prior art developments utilizing each of the types of such processes are hereinafter described.
A system having a regenerative heat exchange design was disclosed in U.S. Pat. No. 3,456,718 by Jan R. de Fries, issued Jul. 22, 1969. That system incorporates a special disc-shaped heat exchanger that rotates within a blower unit between two separate air streams. The heat exchanger is heated by the hotter of the two air streams and rotated into the cooler of the two air streams where the heat is released. Such a system is effective for transferring heat, but has the distinct disadvantage of constantly intermixing the two air streams and of being limited to only preheating or precooling of the conditioned air. In other words, the de Fries system is ineffective in providing dehumidification. As a result, practical applications of the system have generally required integration of desiccant wheels into the designs to provide dehumidification of the air being conditioned. Such desiccant wheels function by absorbing unwanted moisture from the conditioned air and, as the wheel is rotated into a very hot air system, by releasing that absorbed moisture through the process of evaporation thereby drying the desiccant material in preparation for the next cycle.
Prior art systems that incorporate desiccants within fresh air make-up provisions in a regenerative heat exchange apparatus include U.S. Pat. No. 4,513,809 issued Apr. 30, 1985 to Steven L. Schneider et al, which discloses both a rotating desiccant wheel and a rotating heat exchanger matrix; U.S. Pat. No. 5,548,970 issued Aug. 27, 1996 to Robert A. Cunningham, Jr., et al, which discloses a rotating desiccant wheel in a refrigeration system to improve air conditioning of supply air but which makes no provision for recovering energy from the exhaust air; U.S. Pat. No. 4,887,438 issued Dec. 19, 1989 to Milton Meckler, which discloses a system for only cooling and dehumidification wherein a desiccant wheel is used with a refrigerant-type air conditioning system and wherein heat from cooling the supply air is transferred to the exhaust air to regenerate the desiccant; and U.S. Pat. No. 5,003,961 issued Apr. 2, 1991 to Ferdinand K. Besik, which discloses the use of a solid, non-movable desiccant and heat exchange matrices through which air flows of exhaust air and then supply air are alternately counter flowed, with final heating being provided by a combustion heater and cooling being provided by a refrigerant-type air conditioner. Systems based on desiccant exchangers are generally expensive to produce and operate and offer only a limited service life before the heat exchange and/or the desiccant media must be replaced. Such designs have primarily been used on small scale applications.
Another regenerative heat exchange system is disclosed in U.S. Pat. No. 3,698,472 issued Oct. 17, 1972 to Harold E. Gold et al, wherein a continuous blanket-type heat exchange media is continuously tracked therethrough with basically the same advantages and disadvantages as previous disk-type systems. Because of the complexity of operation and a high maintenance factor associated with this design, minimal demand has been realized in the marketplace.
Prior art recuperative heat exchange systems that incorporate desiccants within fresh air make-up provisions include U.S. Pat. No. 3,623,549 issued Nov. 30, 1971 to Horace L. Smith, Jr., which utilizes multiple, independent heat exchangers for transferring heat in one direction only, namely from a very high temperature source of air (i.e., 500.degree. F.) to a very low temperature source of air (i.e., 32.degree. F.). Each of the multiple units consisted of two liquid-to-air heat exchangers connected by piping, a liquid pump and a flow control valve, sometimes referred to in the industry as "run-around coils". Single run-around coils have been used for decades in applications for transferring moderate heat between fresh air and exhaust air supplies. However, the Smith application required transferring heat between a very high temperature and a very low temperature for which a single heat transfer fluid could not be used without either boiling-off or freezing-up. By staging the run-around coils, the Smith approach was able to use heat transfer fluids having different boiling and freezing properties which permitted dividing the difference between the two extreme temperatures into acceptable ranges of operation. Although such a design is effective for pre-heating fresh air, it is significantly less efficient in pre-cooling the fresh air and ineffective in removing humidity. As a result, the Smith multi-coil design is generally only applicable to certain highly specialized industrial applications.
Another recuperative design was disclosed in U.S. Pat. No. 3,968,833 issued Jul. 13, 1976 to Ove Strindehag et al, which incorporates a run-around coil design that integrates a secondary liquid-to-air and liquid-to-liquid heat exchange loop to help prevent freeze-up and to boost the temperature of the supply air stream. Heat is supplied to the secondary heat exchange loop by an external source, such as a boiler. Unfortunately, this design has all the disadvantages of other run-around coil designs with regard to cooling and dehumidification.
Another recuperative run-around coil design was disclosed in Patent U.S. Pat. No. 4,061,186 issued Dec. 6, 1977 to Ake Ljung, wherein a unique liquid-to-liquid refrigeration system is incorporated into a complex run-around coil design in order to boost the operating temperatures of the system and enable it to provide a certain level of cooling and dehumidification. Although this approach expands the operating parameters of this type of run-around coil design, the disadvantages include high initial costs, less than optimum efficiency, and expensive and time demanding maintenance of both of the complex liquid and refrigerant systems. A similar system is disclosed in U.S. Pat. No. 4,510,762 issued Apr. 16, 1985 to Fritz Richarts, wherein a combustion engine is utilized to drive a heat pump with waste heat from the combustion engine being used to provide additional heating for the supply air.
Another run-around coil system was disclosed in U.S. Pat. No. 4,142,575 issued Mar. 6, 1979 to Walter P. Glancy, wherein a complete, packaged system for providing fresh air make-up with exhaust air capabilities, sometimes referred to in the industry as a "make-up air unit". A simple, liquid run-around coil is used to precondition the fresh air supply. An earlier patent granted to Walter P. Glancy, namely U.S. Pat. No. 3,926,249 issued Dec. 16, 1975 disclosed another simplistic ventilation system that employs a run-around coil design which, unfortunately, has all the limitations of his earlier run-around coil systems but which did provide an inexpensive heat recovery option with a reasonable economic benefit.
Another design disclosed in U.S. Pat. No. 4,332,137 issued Jun. 1, 1982 to Richard S. Hayes, Jr. utilizes two independently controllable heat pumps, one for heating and the other for cooling. The Hayes, Jr. system, however, does not provide fresh air makeup and does not provide heat recovery.
U.S. Pat. No. 4,742,957 issued May 10, 1988 to Stephen Mentuch utilizes a heat pipe-type of heat exchanger in a fresh air make-up system, a system which would have operating characteristics comparable to those of a run-around coil system. Although the heat pipe design simplifies both production and operation of the system and reduces maintenance requirements thereof, this system has the disadvantage of not being very effective for dehumidification purposes.
An alternative to the heat pipe pre-conditioner design for ventilation purposes may utilize an expanded plate-type heat exchanger wherein the expanded plate heat exchanger comprises a series of thin metal plates that are configured to form numerous independent flow passages for each air stream. The result is efficient conductive heat transfer between the air streams. A example of such a heat exchanger is disclosed in U.S. Pat. No. 5,000,253 issued Mar. 19, 1991 to Roy Komarnicki.
Another concept was disclosed in U.S. Pat. No. 5,179,998 issued Jan. 19, 1993 to Nicholas H. Des Champs, wherein two efficient expanded plate heat exchangers and a conventional refrigeration unit are used to provide a fresh air make-up system for a swimming pool enclosure. A standard air source refrigerant coil is integrated into the system to control the level of humidity. If necessary, an optional heater is provided to heat condition the make-up fresh air after passing through both plate heat exchangers and the refrigerant coil. This system is typically quite expensive, especially when applied to a corrosive pool environment. Further, the bulkiness of the plate heat exchangers largely restricts the use of this system to large scale applications.
Relatively recently, some prior art designs have attempted to combine both recuperative and regenerative technologies into a single complex system. An example thereof is disclosed in U.S. Pat. No. 5,579,647 issued Dec. 3, 1996 to Dean S. Calton et al, which system provides only central air conditioning and dehumidification but which, with minor modification, could function as a make-up air system. This design combines a rotating desiccant wheel, a rotating heat exchanger, and a single-refrigerant air conditioning circuit with multiple condensers and evaporators. The heat rejected from the air conditioning condenser coils is used to rejuvenate the desiccant dehumidifier wheel. Though this system does provide cooling and dehumidification, albeit at high initial cost and operating expense, it does not provide heating. Similar designs were disclosed in U.S. Pat. No. 5,325,676 issued Jul. 5, 1994 to Milton Meckler which incorporates a heat pipe exchanger in lieu of the rotating heat exchange wheel, and U.S. Pat. No. 5,471,852 issued Dec. 5, 1995 to Milton Meckler that utilizes a liquid desiccant, a heat pipe exchanger, and a refrigerant air conditioner with a desuperheater for rejuvenating the desiccant liquid.
Conventional reverse cycle heat pump technology has become a standard method of providing heating and cooling to building environmental spaces as well as process loads in industrial processes. These systems have proven to be relatively effective and efficient throughout a broad climatic region of the United States. The acceptance of heat pump systems over the past three to four decades testifies to the growing success of this technology. Heat pump systems have also made inroads into the make-up air technology as well.
As for heat recovery, an example of such a feature in a basic heat pump circuit is disclosed in U.S. Pat. No. 5,348,077 issued Sep. 20, 1994 to Chris F. Hillman.
Still, such prior art systems have not provided cooling, heating, dehumidification, and heat recovery in a single system with the desired capabilities, efficiencies, and control. What is needed is a single system that does provide the desired capabilities, efficiencies, and control.